Top Ten Biggest Oil Reserves in the World

1. Ghawar. Saudi Arabia. 30 Billion Barrels.

The once and future king. Ghawar is thought to have had more than 100 billion barrels of recoverable oil in place. At 160 miles long and 16 miles wide it boggles the mind of even the most experienced geologists. With something on the order of 60 billion produced over the past 60 years, you'd be excused for thinking that Ghawar was sliding into its twilight years. Yet the Saudis insist that Ghawar is still going strong, producing 4.5 million bpd from six main producing areas with the ability to do 5 million bpd if called upon.

2. West Qurna. Iraq. 21 Billion Barrels.

This month a joint venture between ExxonMobil and Royal Dutch Shell were awarded the contract to develop the 9 billion barrel first phase of the West Qurna oil field. They will aim to raise output from 300,000 bpd to 2.3 million bpd. It's tough to make the case that the two biggest oil companies from the countries that invaded Iraq in 2003 are getting a sweetheart deal. The contract calls for the government of Iraq to retain ownership of the field and the oil.

3. Majnoon. Iraq. 13 Billion Barrels.

Massive reserves in a relatively small area near the Euphrates River in southern Iraq, the field's abundance was so mind-boggling that it was named Majnoon, Arabic for "crazy." This easy oil hasn't been developed in part because of its location so close to the Iranian border. In the 1980s, during the Iran-Iraq war, managers reportedly buried the wells, concerned that they might be targeted by Iranian forces. The field produces just 50,000 bpd now but has the potential to do 1.8 million bpd.

4. Rumaila. Iraq. 17 Billion Barrels.

In November, British giant BP and China National Petroleum won the first oil contract of the post-Saddam era to redevelop Rumaila. Located on the border with Kuwait, the field is already producing 1 million bpd, half of Iraq's total production. The partners intend to spend some $15 billion to treble that to 2.85 million bpd. That output would be enough to put Rumaila in second-place worldwide after Saudi Arabia's Ghawar.

5. Khuzestan. Iran. 100 Billion Barrels?

Not just a field, Khuzestan is the province where 90% of Iran's oil is produced. It borders Iraq and is home to the Ahwaz field, thought to produce 300,000 bpd, and the Yadavaran field, which is being developed by China's Sinopec under a $70 billion deal made in 2004. Last year in the province Iran trumpeted the discovery of an 8 billion barrel field called Soussangerd. Iraq's Majnoon field is thought to extend over the border into Khuzestan territory.

6. Kashagan. Kazakhstan. 9 Billion Barrels.

Discovered in the Caspian Sea in 2000, Kashagan has recoverable reserves of more than 9 billion bbl out of total oil in place of some 38 billion bbl. The reservoir is deep (15,000 feet), the oil is highly corrosive (19% hydrogen sulfide), and getting it is costly ($100 billion-plus in expected project costs). Production is expected to reach 1.5 million bpd by the end of the decade.

7. Khurais. Saudi Arabia. 27 Billion Barrels.

Last year Saudi Aramco put the finishing touches of the $10 billion development of Khurais. This included pipelines to bring 2 million bpd of seawater for injection under the field. This water injection, a technique perfected by the Saudis at Ghawar, is the key to Khurais and its 1.2 billion bpd of output. The field was partially developed in the 1980s with peak production on the order of 140,000 bpd. The reservoir is huge, but because of its complexity this oil is not "easy" like the untapped Iraqi fields.

8. Tupi. Brazil. 8 Billion Barrels.

Discovered off Rio de Janiero in 2006, the Tupi field was revolutionary for Brazil, the first of a rash of mega-discoveries including Jupiter and Carioca that have established the region as one of the world-class oil and gas basins of the world. The fields, in general, are under more than one mile of water, three miles of sand and rock, then another mile of solid salt. Because the salt layer scrambles the signals of seismic testing gear figuring out where to drill the well was extremely difficult. Costly too, at roughly $100 million per well.

9. Carabobo. Venezuela. 15 Billion Barrels.

Bidding on seven blocks in the Carabobo section of Venezuela's Orinoco heavy oil belt will take place at the end of January. The blocks up for bid contain some 15 billion barrels of heavy, tar-like oil. Similar to Canada's oil sands, there's no exploration risk--everyone knows the oil is there, it's just a matter of getting it out. Despite his feverish nationalization of oil fields, banks and retail stores, Venezuela's President Hugo Chavez knows that he needs foreign capital and expertise to unlock the heavy oil.

10. North Slope, Alaska. 40 billion barrels?

By 2025, without new development, North Slope oil output will decline to the point that there won't be enough oil to keep the Trans-Alaskan Pipeline System running. A 2008 Department of Energy study found that the North Slope, including the National Petroleum Reserve parts of the Alaska National Wildlife Refuge and offshore Beaufort and Chukchi Seas could yield nearly 40 billion barrels of oil and more than 125 trillion cubic feet of gas. BP, ExxonMobil and others are itching to build a $30 billion pipeline to carry gas down to the Lower 48. Without political support, it won't happen.